This invention relates to apparatus for tensioning a safety belt, and in particular to such apparatus wherein tension is applied by piston displacement in a working cylinder in response to gas pressure. In such devices it is desirable to provide a mechanism for preventing reverse motion of the piston after completion of the tension action.
In order to avoid personal discomfort, very often safety belts are applied by vehicle occupants with rather loose tension. Maximum safety for the occupant, however, necessitates that the safety belt be applied rather firmly to provide restraint in the event of an accident. In U.S. patent 3,871,470, Schwanz has described an apparatus for increasing the tension of a safety belt in response to a vehicle accident. This type of apparatus operates with a vehicle mounted sensor, which in response to the occurrence of an accident provides a signal, which detonates an incendiary device to provide gas pressure. The pressure from the incendiary device causes a piston within a cylinder to be moved, thereby applying tension to the safety belt. The apparatus described by Schwanz includes a reverse stop clamping device acting similar to a free wheel and consisting of griping jaws in ring shaped arrangement about the piston rod. The griping jaws described by Schwanz are located in a conical housing arranged such that the reverse motion of the piston causes blocking of the griping jaws into position. The device as described by Schwanz contains a comparatively large number of parts, many of which must be accurately machined with high quality finishes and narrow tolerances. Production of the Schwanz device is therefore considerably expensive.
Another seat belt tensioning device is described by Schwanz et al. in allowed U.S. patent application Ser. No. 572,328, filed Apr. 28, 1975 now U.S. Pat. No. 3,951,430. The device described in Schwanz's later application includes a less expensive reverse motion blocking device, but only provides for blocking of the piston in one position.
It is therefore an object of the present invention to provide apparatus for tensioning a safety belt with a reverse motion blocking mechanism, which is simple and inexpensive to construct.
It is a further object of the present invention to provide such a belt tensioning apparatus with a reverse blocking mechanism which will provide blocking of the tensioning device in a plurality of blocking positions.